The Austrian pianist Friedrich Gulda (1930-2000) was never one to be reined in by convention. As a performing musician he wore many hats, and I'm not just referring to the stash of Bukharian headgear he wore for his concerts. He was a classical pianist, composer, jazz player and even, at one time, recorded as a vocalist under the pseudonym "Albert Golowin". He played the piano, the baritone saxophone, percussion instruments and a bass wooden recorder. He could rightly be described as an eccentric, reportedly once performing a concert in the nude and, in 1999, faking his own death in what some regarded as a tasteless publicity stunt.

This latest release from Berlin Classics gives further credence to his desire to extend his musical horizons. As a notable Bach player, he was aware that, in addition to the organ, the clavichord was a great favourite of the composer, so considered it logical to perform his works on one. According to Bach’s first biographer, Johann Nikolaus Forkel, the clavichord let him ''express his most refined thoughts'' with its ''variety in the gradation of tone”. On the first half of the CD a Widmayer clavichord is used. Its particular character is intimate and refined. In contrast, the second half is played on a Neupert, advancing a bigger, more powerful sound. Gulda had a working knowledge of the two instruments over a period of five years. We can hear the individual personalities of each on this disc.

Gulda had been drawn to the instrument back in the 1970s via Paul and Limpe Fuchs, whose ensemble Anima-Sound had featured their own home-built instruments at his festival in Ossiach in 1971. By the end of the 70s he was giving public performances on the instrument. He experimented with amplification of the instrument in a concert setting, finally settling on a microphone placed directly over the strings.

I was fascinated reading about the restoration of these recordings. They date from 1978-1979 and were taped by the pianist to monitor both his playing at concerts and his morning's practice. When the tapes arrived on the desk of Christopher Stickel, the producer and audio restorer, they were in a poor state of health, with many stuck together. Stickel's painstaking work included an initial "baking" procedure to enable them to be played. Elimination of hum, crackles and jumps was dictated by the governing principle of as little intervention as possible. There's no doubting his tremendous success in restoring these valuable audio documents of a great artist to the public domain. He's given them a new lease of life.

I haven't listened to too much clavichord playing, and it's certainly an acquired taste. Without going into too much detail, a metal "tangent" attached to the key, strikes the string and makes it vibrate. The key stays in contact with the string enabling the finger to vary the tone, even adding vibrato. The sound produced is sweeter and less muscular than the harpsichord. Its upper range is dulcet, whilst the lower delivers a metallic buzz. This allows the performer an enormous range of nuance. What attracts me is the clarity and definition of the contrapuntal lines, a definite plus in Bach playing.

In the first half of the disc we are told that Gulda is playing a Widmayer, with the quality of recording markedly different to that of the second. The instrument sounds brighter and more sharply profiled. In the second half the sound is warmer; I prefer the richer and rounded tone of the Neupert. Gulda's Bach playing is rhythmically buoyant and exiting. The crisp incisiveness and delineation of polyphonic lines, similar attributes I find in his traversal of the complete Well-Tempered Clavier, are compelling. I would take exception with the speeds of three works on the disc. The E minor Prelude of Book 2 (WTC) is rushed and sounds frenetic and garbled. The opening Prelude and the Bourrée of the Second English Suite are too much of a mad dash for my liking, and sound as if played on automatic pilot. On a plus note, the chromatic Fantasy and Fugue sounds truly improvised, with the pearl-like runs of the Fantasy sparking and effervescent.

This has been, without doubt, a labour of love for all concerned, and those admirers of Gulda's art, like myself, will find much to savour. My own feelings are that this release will be restricted mainly to the niche market, appealing especially to aficionados and Gulda completists.